1. Field of the Invention
This invention relates to the field of methods and chemicals for control of nematodes and other soil-borne pests, and particularly to a method using furfural as a nematicide.
2. Description of the Prior Art
Nematodes are slender, worm-like organisms found in the soil almost anywhere in the world. Nematodes reproduce bisexually and by parthenogenic or hermaphroditic reproduction which result in eggs, and then typically progress through four juvenile stages to adulthood.
A significant segment of the world's nematodes are plant parasitic, and more than one thousand species of nematodes are known to be harmful to plants. Most plant parasitic nematodes range from 0.5 to 3.0 mm in length. Many plants are affected by nematodes, including soybeans, peanuts, cotton, tobacco, strawberries, root crops, ornamentals, mint, alfalfa, squash, potatoes and many other crops. Nematodes feed on the roots and lower stems of plants, and some attack the leaves and flowers. Some species of nematodes inadvertently introduce pathogenic, root-invading microorganisms into the plants while feeding. Nematodes may also predispose plants to other disease causing agents, resulting in wilts and root rots. In other instances, the nematodes themselves cause the disease, disrupting the flow of water and nutrients in the xylem system, resulting in deprivation of the above-ground parts, and subsequently causing stunting and reduced fruitfulness. Symptoms of nematode infestation include swellings, thickenings, galls and distortions of above-ground components of the plant, and root conditions such as short stubby roots, lesions (dead spots), swellings, galls and deterioration of the plant. See, "The Mutagenicity of Pesticides" by Samuel S. Epstein and Marvin S. Legator, MIT Press, 1971.
The extent of crop loss to nematode infestation is substantial and widespread. The yield losses in agricultural crops in the United States and throughout the world are enormous, and have been labelled as "appalling" by experts in the field.
There is a substantial need for additional chemical controls to limit the damage caused by nematodes and to curb their spread to uninfested fields, especially now because some effective materials have been withdrawn from the marketplace. Nematicides have been available in the prior art, some of which were useful as fumigants. The most effective and widely used control agents have been methyl bromide and EDB (ethylene dibromide), and certain chlorinated compounds including D-D (1,3-dichloropropene-1,2-dichloropropane), DBCP (1,2-dibromo-3-chloropropane), and Telone (1,3-dichloropropene). Other nematicides generally fall within three groups: (1) organophosphate insecticides, (2) isothiocyanates, and (3) carbamate or oxime insecticides. In U.S. Pat. No. 5,013,762 (Ser. No. 442,314, filed Nov. 28, 1989), issued to Smith et al. on May 7, 1991, the use of bromonitromethane as a nematicide has recently been described.
Some of the better known nematicides have been in use for many years. The nematicidal properties of DD and EDB, for example, were discovered in 1943 and 1945 respectively, and effectively launched the use of fumigant nematicides on a field-scale basis. Prior to the 1940's only seedbeds, greenhousebeds, and potting soil had been treated using materials such as chloropicrin (trichloronitromethane), carbon disulfide and formaldehyde. These were very expensive, in some instances explosive, and usually required a surface seal because of their relatively high vapor pressures. See, "The Pesticide Book" by George W. Ware, W. H. Freeman & Co., 1978.
Many of the time-tested nematicides, however, have fallen by the wayside because of carcinogenicity, toxicity and environmental problems. DBCP, for example, was found to be relatively inexpensive and effective, but has been removed from the market because of a tendency to reduce sperm counts in males, and also because of mutagenic activity. Methyl bromide, a highly effective product, is lethal to plant and animal life, and therefore should be used at least two weeks before planting to avoid its total phytotoxic effect. Attempts to substitute non-fumigants have been mostly unsuccessful because of the expense or the limited efficacy of those materials.
Reference to other chemical pesticides has not proven to be very helpful. There are numerous forms of pesticides adapted to the treatment of particular pests. These include, for example, insecticides, herbicides, fungicides, rodenticides, bactericides, acaricides, algicides, miticides, molluscicides, avicides, slimicides, piscicides and ovicides, as well as disinfectants, growth regulators, defoliants, desiccants, repellents, attractants and chemosterilants. The operation of the different types of pesticides varies according to the pests being treated. For example, the known or suspected major modes of chemicals for treating plants (including herbicides, fungicides, etc.) include: (a) inhibition of photosynthesis, (b) inhibition of oxidative phosphorylation, (c) hormone analogs, (d) inhibition of pantothenate synthesis and (e) inhibition of porphyrin, hence of chlorophyll synthesis. In contrast, the operation of chemicals for the treatment of animals (insecticides, nematicides, etc.) include: (a) inhibition of acetylcholinesterase, (b) inhibitions of neuromuscular junction and (c) neurotoxication. There have consequently been a vast number of known pesticides covering a large variety of chemicals operating in differing fashions. However, few effective nematicides have been discovered in the prior art.
There has therefore remained a longstanding and substantial need for a nematicide which is effective, and does not have the disadvantages of the prior art chemicals. The elimination of cheap, effective fumigant nematicides and the poor performance of remaining controls are forcing some crops out of production in the traditional nematode-infested areas of the United States. Also, some nematodes are beginning to appear in areas never before troubled by these pests, as evidenced by the appearance of the soybean cyst nematode in the midwestern United States. While the need continues to grow, concerns over the inherent human toxicity of contact nematicides, and environmental problems from high rates of application (such as leaching into ground water) will result in the restriction of some of the remaining known products.
The present invention is based upon the discovery that furfural is effective as a nematicide, and does not have the high expense or human toxicity associated with certain prior art compounds. Furthermore, furfural is a natural product readily extracted from a wide variety of vegetation, and is known to occur naturally in products routinely consumed by humans. Heretofore, furfural has been indicated as useful for a variety of purposes, including as a fungicide or weed killer. See, The Condensed Chemical Dictionary, Van Nostrand Reinhold Co. (10th Ed. 1981). Also, there are reports in the literature of aromatic aldehydes having antimicrobial and antifungal properties. Benzaldehyde and cinnamaldehyde have been reported as insecticides for use on stored grain. However, it is believed that none of the latter described aldehydes have ever been used commercially. See, Proceedings of the Association for Plant Protection of Kyushu 1987 by Ishibashi, N and Kubo, H. at Saga University, Japan.